Research On Hydration Process And Microstructure Of Thin Layer Cement Paste Modified With Cellulose Ether

At present, urbanization in our country is in a rapid growth. External thermal insulation system is main technical approaches of building energy efficiency. Adhesive mortar and anti-crack mortar play an important role in protecting energy-saving effect and durability. Against this background, it has especially important significance of research of hydration key problems of thin layer mortar. The research was funded by National science and technology support project (No.2011BAJ04B02)" and Youth Fund of National Natural Science Foundation of China (No.50902107)". In multiple factors environment, kinetics of hydration process of cement paste modified with cellulose ether (CE) was verified by the research of rheological properties and heat-electrical characteristics. According to different service environment of cement paste, hydration mechanism of cement paste was studied under the condition of rapid water loss. To elaborate hydration characteristics of thin layer cement paste modified with CE, the model of hydration process and interface transition zone microstructure of thin layer cement paste modified with CE was established based on rheological properties, kinetics of hydration process and hydration mechanism under the condition of rapid water loss of cement paste modified with CE.The main research and obtained important achievement of this article as follows:1. Based on rheological behavior of CE in aqueous solution (mixing stage environment) and (hydration stage environment),film-forming process of CE and influence of solution environment (temperature, pH, ion species and valence) on rheological behavior of aqueous solution and cement pastes were studied. Film-forming process of CE in different liquid phase environment and mechanism of temperature, pH, ion species and valence were obtained.Apparent viscosity, shear stress, yield stress and plastic viscosity were used as index system. The influence of kind and dosage of CE on rheological behavior was studied. Rheological properties of aqueous solution and cement paste which modified with CE were discussed under different temperature and pH. At the same time, the lower critical solution temperature and isoelectric point of CE were obtained. The sensitivity of HPMC, HEMC and HEC to pH is different. The influence of cations, anions and its valence on apparent viscosity of CE solution was respectively studied. Mechanism of ions species and valence was expounded based on lyotropic series and revealed the film-forming characteristics of CE in complex liquid phase environment. Theoretical basis was provided for studying the rheological properties of cement paste modified with CE in plastic stage.2. Design and preparation methods of kinetics of hydration process of cement pastes modified with CE and cohesion water and slow release components (CWRC) were put forward. Based on hydration exothermic rate curve and derivate of resistivity curve of cement hydration, macro thermal effect and electrochemical characteristics change rule of early stage of cement hydration were mastered and the relationship among hydration exothermic, resistivity and cement hydration process was studied. Heat-electric model of system composed of CE, CWRC and cement was established.The influence of CE and CWRC on hydration exothermic and resistivity of cement pastes was studied and delay effect of CWRC was less than CE on each stage of cement hydration was pointed out. It had linear dependence among Ca (OH)2content, chemically combined water content, hydration heat quantity and resistivity. A new structure parameter was provided to describe structure formation and hydration process. Heat-electric model of system composed of CE, CWRC and cement was established by analysis of hydration exothermic rate curve and derivate of resistivity curve of cement hydration. The process of cement hydration was divided into solution-precipitation equilibrium stage, structure formation stage, structure development stage and structure stability stage. It had a good consistency that description of hydration exothermic rate and derivate of resistivity on hydration kinetics process of cement in early stage. Instantaneous state of structure formation and process of cement hydration could be accurately described.3. Trial design and evaluation methods of thin layer cement pastes modified with CE under rapid water-loss were first proposed. Water loss characteristics, interface properties and microscopic analysis were studied of cement pastes modified with CE in early stage by change of thickness of cement pastes, curing temperature and kinds of matrix materials. Hydration mechanism and principle of microstructure formation of thin layer cement pastes were found out. Water-loss speed and water-loss rate were used as assessment criteria to study water-loss characteristics and mechanism of thin layer cement pastes under rapid water-loss. The influence of thickness of cement pastes, curing temperature and kinds of matrix materials on interface properties of thin layer cement pastes and described interface damage form of different ages. Hydration law of thin layer cement pastes under rapid water-loss was studied by XRD, FTIR and TG-DSC. Distribution regularities of hydration products along the thickness direction of cement paste were proved by microanalysis of surface layer, interlayer and interface layer of cement pastes under rapid water-loss. Principle of interfacial damage of thin layer cement paste was revealed and laid a theoretical basis for analysis of insulation layer drop and covering layer empty drum and cracking of external thermal insulation system.4. Based on water and ion migration, CE film formation and hardening process of cement paste of thin layer cement pastes modified with CE, distribution regularities of hydration products along the thickness direction of cement paste were analyzed. The model of hydration process and interface transition zone microstructure of thin layer cement paste modified with CE under actual service environment was established.The model of hydration process of cement paste modified with CE under actual service environment was established according to CE film formation and dissolve process, water-loss mechanism and ion migration process, hydration process and microstructure, distribution regularities of hydration products. Characteristics water-loss, changes of interface microstructure, kinds and amount of hydration products were analyzed on the basis of pore structure and water absorption of substrate materials and model between interface transition zone microstructure and matrix material of thin layer cement paste was established. It had important theoretical and practical significance of research on hydration mechanism of thin layer cement pastes modified with CE.